JPH07119866B2 - Lens body - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording / reproducing method for recording or reproducing information by focusing light emitted from a light source such as a laser on a disc-shaped recording medium (hereinafter referred to as a disk). The present invention relates to a lens body used in an apparatus.

2. Description of the Related Art A conventional lens body is disclosed in, for example, Japanese Patent Application Laid-Open No. 58-68248. FIG. 6 shows, among the lenses of this conventional example,
It is a block diagram of the optical pickup used for the objective lens which focuses light on a disc surface.

Reference numeral 20 is a light source, 26 is a disk, and 25 is an objective lens body for converging a light beam on the surface of the disk 26. Further, 29 is an objective lens 25, a polarization beam splitter 23, and a photodetector 28.
Is a movable lens barrel portion for storing the. The objective lens body 25 is configured by accommodating a plurality of lenses in a cylindrical lens barrel having a constant diameter.

The optical axis positioning of the objective lens body 25 is extremely important in the optical recording / reproducing apparatus.

First, if the optical axes of the disk 26 and the objective lens body 25 are not orthogonal to each other, asymmetrical aberrations such as so-called astigmatism and coma are generated, and recording / reproducing characteristics are significantly deteriorated.

Secondly, if the optical axes of the light source 20 and the objective lens body 25 do not coincide with each other, not only will the light transmission efficiency be lowered, but the objective lens body will be used off-axis, so aberration will occur. , Deteriorates recording / reproducing characteristics.

Thirdly, the optical axes of the objective lens body 25 and the photodetector 28 are
If they do not match, a focus shift and a tracking shift occur, which deteriorates the recording / reproducing characteristics.

Therefore, the optical axis of the objective lens body 25 is positioned by the movable lens barrel portion.
The optical axis of the objective lens body 25 is positioned by fitting and adhering the outer circumference of the objective lens body 25 to the inner circumference of 29 as a reference.

Problems to be Solved by the Invention In the above-described configuration, in order to improve the optical axis positioning accuracy of the objective lens body 25 having a uniform diameter cylindrical lens barrel, the fitting length of the objective lens is increased. (Long body).

Reduce the clearance of the fitting part (narrower clearance).

 Increase the fitting surface accuracy.

There are three methods.

However, if the length of the fitting portion is increased, deep hole machining that requires dimensional accuracy is required for machining the inner circumference of the movable lens barrel portion.
Processing is difficult and costly.

In addition, increasing the length of the objective lens body causes an increase in the weight of the movable portion, and deteriorates the frequency characteristics of focus control and tracking control.

In addition, narrowing the clearance is necessary for the objective lens 25 and the movable lens barrel.
In addition to making the fitting and assembling work of 29 difficult, there is a case where the adhesive comes out of the adhesive when it is adhered, and the lens part is contaminated.

Further, improving the surface accuracy of the fitting portion immediately leads to an increase in cost.

Furthermore, the optical recording / reproducing apparatus is not limited to this objective lens body. For example, a collimator lens for converting diffused light generated from a semiconductor laser into parallel light, an objective lens body or the like, or an optical axis longer than that. Many lenses that require positioning accuracy are used.

In view of such a point, the present invention improves the optical axis positioning accuracy,
An object of the present invention is to provide a lens body that does not cause a large increase in cost, does not impair the workability and assemblability, and does not significantly increase the weight of the movable portion.

Means for Solving the Problems The present invention relates to a lens system including at least one lens system, a cylindrical lens barrel for housing the lens system, and a guide shaft having a central axis decentered from the central axis of the lens barrel. A lens body having a portion at the end of the lens barrel.

Effect The present invention reduces the fitting clearance of the guide cylindrical portion at the end of the lens barrel by the above-described configuration, and rotates the lens barrel in the fitting portion based on the narrow fitting portion as a reference. The lens optical axis positioning accuracy of the objective lens or the like can be improved by fixing the lens at a position where the fitting clearance of the lens barrel is minimized by means such as adhesion.

Example FIG. 1 is a sectional view of a lens body in an example of the present invention, and FIG. 2 is a rear view of the same. 1 is the lens 1a, 1b, 1c, 1d
2 is a cylindrical lens barrel for housing the lens system 1, 3 is a guide shaft portion having a central axis decentered from the central axis of the lens barrel 2, and 4 is a lens body.

Next, the optical axis positioning operation of the lens body in one embodiment of the present invention will be described using FIG. 3 and FIG.

FIG. 3 is a sectional view for explaining the operation of optical axis positioning of a lens in one embodiment of the present invention, and FIG. 4 is a rear view of a positioning reference portion such as a movable lens barrel portion with respect to an objective lens body.

Reference numeral 5 is a positioning reference portion including a fitting hole 5a into which the lens barrel portion 2 is fitted, a reference hole 5b into which the guide shaft portion 3 is fitted, and a light transmitting 5c through which light passes.

First, the guide shaft portion 3 is inserted so as to fit into the reference hole 5b.
Next, the lens barrel 2 is rotated around the reference hole 5b.
At this time, since the central axes of the lens barrel portion 2 and the guide shaft portion 3 are eccentric, there is a position where the clearance between the fitting hole 5a and the lens barrel portion 2 becomes almost zero due to this rotational movement.

FIG. 5 is a control diagram showing this state. The two-dot chain line in the drawing shows the initial state, and the hatched portion shows the state in which the clearance between the fitting hole 5a and the lens barrel 2 has become almost zero due to the above rotational movement.

The optical axis is positioned by fixing the lens 4 to the positioning reference portion 5 at this position by means such as bonding.

As described above, according to the embodiment of the present invention, since the guide shaft portion 3 having a smaller diameter than that of the lens barrel portion 2 is used as a reference, it can be easily compared with the lens barrel portion 2 having a large diameter. The dimensional accuracy can be improved. Therefore, the depth of the reference hole 5b can be made shallower with respect to the required accuracy of the optical axis compared with the case where the lens barrel portion 2 is lengthened, so that the difficulty of deep hole processing can be reduced and the fitting and assembling work can be performed. Does not impair sex.

Further, as compared with the case where the entire lens barrel portion 2 is lengthened, an increase in weight can be suppressed, so that frequency characteristics of focus control and tracking control are less likely to deteriorate.

Even if the fitting clearance between the guide shaft portion 3 and the reference hole 5b is narrowed, if the place where the bonding is performed is the clearance between the lens barrel portion 2 and the fitting hole 5a, the lens will not be removed due to the adhesive sticking out. It can prevent pollution.

Furthermore, since the surface area of the portion requiring surface accuracy can be limited to the guide shaft portion 9 and the reference hole 5b, the surface accuracy can be improved at low cost.

As described above, according to the present invention, the lens barrel portion is eccentrically rotated with reference to the small-diameter guide shaft that is eccentric with respect to the lens barrel portion, and the clearance between the lens barrel portion and the fitting hole is reduced. Almost 0
The optical axis positioning accuracy can be improved by fixing the lens at the position.

Therefore, it does not cause a large increase in cost, does not impair the workability and assemblability, and can suppress the increase in weight, so that the frequency characteristics of focus control, tracking control, etc. are less likely to deteriorate, and the adhesive does not come out. It is possible to provide a lens body capable of improving the optical axis positioning accuracy by preventing the lens from being contaminated.

[Brief description of drawings]

FIG. 1 is a sectional view of a lens body in one embodiment of the present invention,
2 is a back view of the same embodiment, FIG. 3 is a cross-sectional view for explaining the optical axis positioning operation of the same embodiment, FIG. 4 is a configuration diagram of a positioning reference portion of a lens of the same embodiment, and FIG. FIG. 6 is a plan view for explaining the optical axis positioning operation of the same embodiment, and FIG. 6 is a configuration diagram of an optical pickup using a conventional lens body. 2 ... Lens barrel, 3 ... Guide shaft, 5a ... Lens barrel fitting hole, 5c ... Reference hole.

Claims (1)

[Claims] 1. A lens system comprising at least one lens system, a lens barrel for accommodating the lens system, and a central axis decentered from the central axis of the lens barrel. And a guide shaft portion provided at an end portion of the lens body.